In the first two sentences, the preterit and imperfect should be switched. In the third sentence, I am ok with the imperfect tense, but it seems that hablaba (was talking) would be better than decía (was saying).
The last line does not look like a complete sentence to me. It contains a future subjunctive of discutir. I can't figure it out.
Actually, I always loved teaching the Preterite vs. the Imperfect. The Imperfect (the easiest tense there is in Spanish) "paints" the background in a story. It focuses on the "middle" of something. We know it had a beginning but we don't focus on that and we never know if it ends. The English meanings are: was/were + -ing, used to + infinitive or simply -ed. yo estudiaba = I was studying, I used to study, I studied. There are 3 translations usually for a verb. In one word, this tense is for "description." ~ ~ ~ (wavy lines representing it)
The purpose of the Preterit (perhaps the most difficult tense to form in Spanish) is for "action." / / / (these lines represent something with a beginning, a middle and an END. We focus on it's being over and done with. The English meanings are 2: did or -ed. yo estudié = I studiED, I DID study.
Do NOT use a translation site. It teaches you nothing and can NOT capture the "nuances" of a language. Besides it usually translates literally (word for word) and turns out to be ridiculous!
Now, the Imperfect only has 3 irregular verbs (ser, ir, ver) and only has 2 sets of endings = ía or -aba. The Preterit has 2 sets of endings for regular verbs = é, as, o, amos, aron OR í, iste, ió, imos, -ieron. However many stems are different in 3rd-person singular and plural (o--->u, e--->i, etc.)
As for your answers, a QUICK answer is of no use, unless you UNDERSTAND what you are doing! Now, for your answers:
yo tuve (no accent, unstressed ending) / comenzó (it DID begin) / discutía (WAS discussING) = why this verb? this doesn't make sense = was discussing a class about sports??? / NOT decir (was saying) but hablar (was talking) = hablaba / I can not do the last sentence for you without knowing EXACTLY what you saw. Were the verbs provided for you that you were to use, or did you have to supply them based upon the MEANING of what you saw? Please type exactly what the instructions were!